Among the conventionally-known internal combustion engines are a premixed compression auto-ignition or self-ignition type in which a compression ratio in a combustion chamber is increased so that an air-fuel mixture supplied to the combustion chamber is automatically or spontaneously ignited by being compressed by a piston.
An example of such premixed-compression-self-ignition-type internal combustion engines is disclosed in Japanese Patent Application Laid-Open Publication No. 2005-69097 (Patent Literature 1), in which the air-fuel mixture can be ignited at a plurality of positions in the internal combustion engine and burned or combusted uniformly by being highly compressed to be automatically or spontaneously ignited. With such an increased compression ratio in the combustion chamber, the air-fuel mixture can be highly compressed and spontaneously ignited without use of an ignition plug (i.e., spark plug). However, with the internal combustion engine disclosed in Patent Literature 1, where the air-fuel mixture is automatically ignited without use of an ignition plug, it is difficult to stabilize the ignition timing.
As a means for stabilizing the self-ignition timing of the air-fuel mixture, it has been known to secure a negative overlap state where both an exhaust and an (air) intake valve are closed in an exhaust stroke to cause a part of combustion gas to remain in the combustion chamber so that heat energy of the remaining or residual gas can be used for combustion of the air-fuel gas. Namely, an internal EGR (Exhaust-Gas-Recirculation) mechanism is employed for mixing the residual combustion gas into the air-fuel mixture, so that the self-ignition timing of the air-fuel gas can be stabilized using the heat energy of the residual combustion gas in a compression stroke (see, for example, Japanese Patent Application Laid-Open Publication No. 2005-201127 (Patent Literature 2)).
However, in the exhaust stroke of such an internal combustion engine, the piston ascends to its top dead center or point with a part of the combustion gas remaining in the combustion chamber. Thus, because the remaining combustion gas is compressed by the piston until the piston reaches to its top dead center, a temperature of the remaining combustion gas would increase to get higher than a temperature of a cylinder wall. Therefore, heat loss from the cylinder wall would increase so that the remaining combustion gas may undesirably lower in temperature.
Further, as the reaches the top dead center in the exhaust stroke, a stress (load) would be generated from the remaining combustion gas to act on the piston by the remaining combustion gas being compressed by the piston. Therefore, the thus-generated stress is transmitted via the piston to the interior (particularly, sliding portions) of the internal combustion engine, so that friction may be produced in the interior of the internal combustion engine.
Further, Japanese Patent Application Laid-Open Publication No. 2007-239555 (Patent Literature 3), for example discloses a multilink-type internal combustion engine where a top dead center of the piston at the time of switching from the exhaust stroke to the intake stroke (i.e., exhaust top dead center) is set different from a top dead center of the piston at the time of switching from the compression stroke to the expansion stroke. In the internal combustion stroke disclosed in Patent Literature 3, the exhaust top dead center of the piston is set higher than the expansion top dead center of the piston. Thus, in the internal combustion engine disclosed in Patent Literature 3, the remaining combustion gas in the combustion chamber would be compressed by the piston more strongly than in the internal combustion engine disclosed in Patent Literature 2, so that heat loss of the remaining combustion gas and friction produced in the interior of the internal combustion engine cannot be effectively suppressed.